Syntax question

I have found this as part of a navigation script.

[code=php]
ul.nav,
.nav ul { …. margin & list-style-type setting … }

ul.nav { … width setting … }

ul.nav>li { … margin & padding setting … }

ul.nav li>ul { … sub-list item settings of width, margin, left, display …}

ul.nav li:hover>ul { … display change … }

nav ul li a { … display changes without hover …}

ul.nav,
.nav ul,
nav ul li a { … color settings only … }

ul.nav li:hover { … color settings only … }

ul { border settings … }

.nav a { … text decoration … }

[/code]

My question is how does the syntax differ in results?
For example
ul.nav,
.nav ul {
looks like both control the same thing (?)
All <UL> with a ‘class=nav”
and
All ‘class=nav’ with <UL> tags are given a paritcular look when rendered.

Is there a purpose for the “duplicated” syntax, or is this just good practice?

Later into the style there is a:
ul.nav>li {
and
ul.nav li>ul {

What does the ‘>’ do in this context and is is different from:
ul.nav li {
and
ul.nav li ul {

The style sheet works well but I just don’t understand the syntax differences
and my references do not dwell on this.

Thanks for any insight. ?

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